Process for preparing hydrocarbons for polymerization



v.Il .me 13, 1944. H. l.. HAYS l-:rALv 2,351,123

PROCESS FOR PREPARING HYDRocARBoNs For;vr PoLYMERIzATIoN Filed May 20,v 1940 v2 She'ets-Sheet 1 koe POLY

DEBUT N I1 ER DEHYDROGE A 33 I INVENTORS HARRISON L. HAYS A'ITORNEY June 13, ,1944; H. L'. HAYs g-:rAL 2,351,123

` l ffRocss FORv PREPARING HYDRoCARBoNs FOR BOLYMERIZATION" Filed may zo, V1940 2 sheets-sheet 2 HARRISON L. HAYS ATTORNEY portion of the unconverted hydrocarbons is separated from this emuent and is passed in the liquid phase as a refrigerant in heat-exchange relationship with vapors being evolved from the top of the fractionating column from which the charge to the olen conversion process has been drawn.

As is more fully brought out hereinafter, this I erick E. Frey in his application Serial No. 305,549,V

filed November 21, 1939 a direct heat-exchange relationship is especially applicable, since the recycled hydrocarbons contain polymerizable olefins, such as propene, which are to be recycled to the polymerization step. In the practice of this modification of our invention, this unreacted material serves a cooperative dual function, that is, as a direct-contact refrigerant and reflux, and as a recycle of unreacted oleflns to'an olefinpolymerization step.

It is an object of this invention to provide a process for the production of a suitable charge stock for a conversion process for the production of normally liquid hydrocarbons from normally gaseous hydrocarbons.

It is another object of this invention to provide a process for the production of, from a normally gaseous hydrocarbon mixture containing undesirable low-boiling material, of a hydrocarbon fraction which is free of that undesirable low-boiling material and which is suitable fora subsequent conversion process to form' hydrocarbons having higher, molecular weights.

Another object of this invention is to provide a process for the utilization of hydrocarbon material available in the eilluent of an olenn-polymerization process to aid in the preparation of a suitable feed stock for the polymerization process.

Further objects and advantages ofV this invention will be apparent from the following description and disclosure.

In one method for practicing the process of our invention, it is preferred to produce a charge stock for a catalytic polymerization step from the eiiluent of a step which involves the dehydrogenation of a mixture of butane, preferably of a mixture which contains predominantly isobutane. With such a mixture, which is vpredominantly isobutane, thermal dehydrogenation is a very satisfactory method of producing suitable olei1n`s for subsequent catalytic polymerization; such an operation does not involve the great expense which is attached to a catalytic dehydrogenation operation. The oleiins produced by such a step consist primarily of propene and'isobutane, with only minoramounts of other hydrocarbons, as well as methane, which is present in an amount substanw tially equivalent to the propene, and unreacted isobutane and hydrogen. -From the efiluent of this dehydrogenation, the hydrogen and methane may be substantiallyv completely removed by a separation which involves only compressionto a pressure between about 100 to 500 pounds per square inch and subsequent cooling. The liquid Y produced by such a separation will contain only small amounts of material lighter than C: hydrocarbons, but in amounts in excess of that desirable for the subsequent polymerization step. Such a liquid is passed to-the mid-section of a fractionating column which is suitably heated at the bottom. From the bottom'ofthe fractionating column a suitable hydrocarbon mixture can 1s described. l'vrom be separated and passed to a polymerization step. The efiiuent of this polymerization step will contain appreciable amounts of unreacted C: hydrocarbons, a portion of which will be propene, as

5 well as unreacted C4 hydrocarbons, which will be predominantly butane. This will be especially truev after the operation of the entire process has reached a steady state with suitable recycle of the C3 hydrocarbons, as is hereinafter described.

These unreacted C: hydrocarbons are separated from the polymerization emuent and are passed,

as a liquid, directly to the top of the fractionating column, wherein they are vaporized to a substantial extent and act as a direct-contact refrigerant and liquid-absorption medium. C3 hydrocarbons which are not so vaporized pass down the column in the liquid state and are subsequently removed from the bottom of the column with the liquid hydrocarbon fraction which is passed to the polymerization step.

It is, therefore, readily seen that even should this Ca hydrocarbon fraction consist primarily only of propene, as4 described by Frey in his aforementioned application, Serial No.- ,305.549,

the amount of this C: hydrocarbon fraction will increase as the polymerization operation reaches a steady state and there will be ample material available to enable the fractionating column to operate satisfactorily. In the event. however,

n' that this yC3 hydrocarbon fraction consists predominantly of propane, in one modification of the present process, this material may be used as an indirect-contact refrigerant, as is more fully described hereinafter, the desired refrigerating effect being produced without introducing it directly into the fractionating column.

Our invention will now be described in connection with Figures 1 and 2 of the accompanying drawings which form a part of this specifi- Al'. cation.

Figure 1 shows diagrammatically one arrange- ..ment of an apparatus suitable for practicing our invention.

Figure 2 shows diagrammatically a modificadl tion of certain parts of the apparatus shown in Figure 1. Only a part of the apparatus shown in Figure 1 is reproduced in Figure 2 and the var*- .ious units thereof are designated by the same reference numerals as are used in Figure 1.

I0 A hydrocarbon stream comprising a butane.

and which may comprise essentially pure isobutane, enters the system through conduit il, and f is compressed to a suitable pressure by pump Il. In many cases where such a butane stream comes ss directly vfrom a fractional distillation. or other separation step, it may be under a pressure sufficiently high so that the pump Il will not be necessary and in such cases this pump may, of course, be omitted. Since a high superatmospheric pressure tends to affect the subsequent dehydrogenation adversely. the pressure should be generally only sumcient to overcome the pressure drop through the apparatus up to the compressor 4|, and to provide a slight superatmosg5 pheric pressure at the inlet to the compressor.

Such a pressure will not need to be in excess of about 200 pounds per square inch and will genl erally be considerably less than that.

The butane stream, at a desired pressure, then Passes throllsh a conduit I2, and through conduit I8 supplied with valve Il, t0 the transfer line heat exchanger Il, whereit passes in indirect countercurrent heat-exchange relationship with the emuent of the dehydrogenatlnn t0 be the heat exchanger Il, the

verted from the heat exchan 1er I5 through thisy by-,pass by proper control o the v alves |4, i1, and 2|, as will be-obvious to those skilled in the art. From the conduit vI3 vthe stream passes through thel coil 23 located in the furnace 24.

When vthe dehydrogenation step is so operatedA that complete thermal dehydrogenation of the hydrocarbon stream. is accomplished, that is to say, substantially no catalytic dehydrogenation takes place, these coils will be of such dimensions that the hydrocarbon stream is heated rapidly to a dehydrogenating temperature of the order of 1000 to 1250 F., and is held within this temperature range for a period of time such that between about l and 40 mol percent of the eilluent material consists of normally gaseous oleiin hydrocarbons. With such a procedure the eilluent of the coil 23 passes through conduitv 25, which is controlled by a valve 26, and sent through heat exchanger l5, conduit 21, cooler 28, and conduit 30 to the scrubber 3|. When it is desired to carry out a catalytic dehydrogenation,v this may be done by opening valve 32 in conduit 33 and valve 34 in conduit 35, thus connecting catalyst chambers 33 into the system, and closing the valve 23.

scrubber`3| through valved line 33y as will be evident to those skilled in the art, and details pertinent to'this modification have `not been shown. 'I'he eilluent of -thefdehydrogenation step i passes from scrubber 3| through a conduit 40 to arcompressor 4|, which compresses this stream to a pressure of between about '15 and 175 pounds per square inch. The compressed stream passes through conduit.42.to a cooler and condenser 4.3, and then throughbonduit 44 to a vapor-liquid separator 45.

Under the pressure developed by compressor 4| and at the temperature effected by the cooler and condenser 43, all of the hydrocarbon material having four carbon atoms per molecule, along with an appreciable proportion of the propene and lighter hydrocarbons, will be condensed and may be removed from the following separa- In the modification illustrated in Figure 1, the I catalyst chambers 36 comprise relatively small tubes illled with a suitable dehydrogenation catalyst and are so arranged that large amounts of hot combustion gases pass over them. With such a modification the relative volume of the coils 23 .is such that the hydrocarbon stream is rapidly heated to av desirable reaction temperature, such as between about 850 and about 1l50 F., and the stream is .then passed directly into contact with the dehydrogenation catalyst in the tubes of chambers 36.` As the dehydrogenationy reaction progresses, heat is absorbed and this is made up by heat transfer from the combustion gases surrounding theseycatalyst tubes, Although only one source of heat in the furnace 24 is shown, it willbe understood that additional burners, or other sources oi' heat solely for supplying heat to the catalyst tubes and the reactions at the desired temperature level, may also be used. The dehydrogenation eilluent passes 'from the catalyst chambers 36 throughvconduit conduit 31, controlled by valve 33. However, it.

has been found that with suitably controlled dehydrogenation conditions there is little if any of such heavier materials formed, and inl such cases there will be no such material to be rev moved by thescrubber. In such cases the scrubber 3| will only be included as a precautionary measure. However, if vsuch materialis present, this removal may be aided by the -use of a heavy absorption oill or other means,` introduced to tor 45 as a liquid stream. This liquid hydrocarbon mixture will also contain a certain amount of undesirable light material, and therefore it is passed from the separator 45 through a conduit 46, controlled by the valve 41, to the fractionating column or poly-feed stripper 50. Gaseous material which has not been condensed to a liquid under conditions which are `present in the separator 45, pass therefrom in the gaseous stage through conduit |20 controlled by a valve. |2I.

If desired, a mixture having a composition similar to that in conduit 46 may be introduced to the system through conduit 49 controlled by a valve 48, and leading into conduit 46. At times, all of the charge stock to the process may be introduced through conduit 49. In such a case,

the dehydrogenation step, if used, will operate only on hydrocarbons which pass through conduit 93, ashereinaiter described.

such as a pressure of about 50 to 175 pounds per square inch, and in such a case an intermediate pump will not be necessary. In some cases it y, may `bedesirable to operate the fractionating colappreciated.

umn 50 at a somewhat higher pressure, such as ,up to about 300 pounds per square inch, and

in such a case a suitable pump may be inserted to be obtained between '15 and 200 pounds per square inch.

WhenA the compression produced by compres- A sor 4| is not suilicient to produce a separation of liquid in separator 45. the charge to fractionator 50 may be-Withdrawn from conduit |21 through conduit |29 and valve |39 which leads to conduit 46, and fractionator 50 will operate above the pressure developed by pump 4|. If, when such a procedure is followed, a small amount of liquid does Yseparate in separator 45, it may be removed through conduit 46 and compressed by a pump, not shown, inserted in 46 ahead of the juncture of conduit- |23,-as will be readily The stripper or separator comprises essentially a conventional bubble-plate fractionating f column which is heated at the bottom by a conventional heating means such as a heating coll 5|. The topof the Iractionating column ls cooled by the vaporization and expansion of a low-boiling hydrocarbon material in the liquid phase which has been separated from a subsequent polymei-ization step. -Such liquid hydrocarbon material. which, in the present instance, may comprise substantially C: hydrocarbons, passes from c of the iractionating column. As one method of operation. this liquid stream of light, unreacted hydrocarbon material may be introduced directly into the top of the separator or fractionating column system, as by means of an expander and spray nozzle 60. as shown. or by any other means known to the art. When this is done, a considerable amount of the stream is vaporized, producing a large refrigeration eiiect which is quite efficient by reason of the direct heat exchange which can be had with the vapor present in the column at that point. Heavier constituents of these vapors are condensed to liquid as a result of this refrigeration, and are directly returned to the column along with unvaporized portions of the stream entering through conduit il. It will be understood that fractional-,ing column 50 is of a conventional typ, with suitable bubble trays or the like, not shown, and operates with a countercurrent ilow of vapors and liquid throughout the column.

Uncondensed vapors which comprise light hydrocarbons, a small amount of hydrogen which was dissolved in the hydrocarbon stream passm8 through conduit v rized'iight hydrocarbon, such as C: hydrocar ns which were introduced throught conduit 51, and only small amounts of heavier hydrocar pass from the fractionating column 50 tlir trolled-by a valve 62, and are mixed with the vapors passing from separator 4I through conduit |20. When the charge to tractionator Il comes principally from the bottom `of separator |26 through conduit III. these vapors passing from the top of fractionating column Il may Y be passed from conduit il through conduit il and valve 6l and introduced into conduit Ill. Some of the unvaporized propene and propane. introduced as a refrigerant and reflux when direct cooling by the C: stream is used, remains as a liquid and is nally removed from a low portion of the fractionating column along with butene and heavier hydrocarbons and these pass through conduit 65. controlled by a valve It,

. and through a pump 61 to Vmeans for converting` these C: and' C4 hydrocarbons to normally liquid hydrocarbons, such as the polymerization chamber 10 shown.

The conversion process is most preferably one of catalytic polymerization, carried out at a pressure between about 50 and 2000 or more pounds per square inch, at a temperature between about 75 and 500 F., butit may 8150 rbe a thermal p0ly.

merization process operating within a temperature range within about 700 to 1100 F. under pressures between 500 and 2500 pounds per square inch or more, as may be desired and permitted by the materials going into the construction of the conversion apparatus. The eiiluent of this conversion passes from chamber or converting means 10 through a conduit 1|, controlled by a valve 12, to a polymer separator .13, which is,

provided with a suitable heating coil 14 atA the bottom and a suitable cooling means Il at the top and supplied withY suitable bubble trays or the like, not shown. Polymers produced by conversion means III are removed from a low Dart l of this fractionating column 'through a conduit v 'il controlled by a valve 11, and may be subsev quently further fractionated and otherwise treatmayv be found most desirable. Lighter h conduit 0I, conhydrocarbon material, which will comprise mainly hydrocarbons having four carbon atoms per molecule and less. passes from polymer separator Il through conduit Il controlled by a valve Il, cooler l2, conduit I3, pump I4 and conduit 85 to further separating means such as the depropanizer I6. This depropanizer is supplied with suitable heating means for the bottom. represented by the coil Il, and suitable cooling means for the top, represented by the cooling coil Il. Hydrocarbons comprising four and more carbon atoms per molecule are removed from the bottom of this depropanizer I8 by means oi a conduit 90, controlled by a valve 9|. and may be removed from the process through valve l2; or any part or all of this hydrocarbon mixture may be reintroduced into the dehydrogenation process by passing it from conduit 90 through conduit 83, controlled by a valve 94, with suitable control of the valve 82.

Vaporous hydrocarbons, such as a substantially C: hydrocarbon mixture, pass from the separator Ii, through a conduit I5, controlled by a valve 86, and are sent through valve l1 and cooler 98 to the accumulator v52 by means of this hydrocarbon fraction has s high content of parafiin hydrocarbon and it is desired to recycle a hydrocarbon mixture which is more rich in oleiln hydrocarbon, the fraction passing from scparator I6 by means of conduit Il and III may be subjected w some sort of olefin concentration procedure, which is not shown but which is well vknown to those skilled in the art. and a more highly concentrated olefin-containing fraction ymay be reintroduced into the process as a liq- -uid to conduit |22, controlled by a valve i, and leading into conduit Il. The accumulator 52 is provided with a suitable venty IUI provided with a valve l, through 'which unreactive vapors and gases may be vented from time to time. or continuously. as may be found desirable.

'I'he material passing as a gas or a vapor from separator 4l through conduit |20, controlled by a valve |2I, contains hydrogen produced in the dehydrogenation step along with some methane and other light hydrocarbons and also along with some of the heavier, normally gaseous hydrocarbons, such as'propene and butene, which it is desired to incorporate as a part of the charge stock to the polymerization step just described. To this material is added vapors from the fractionating column Il passing through conduit Il, and the resultant mixture is compressed by a compressor |22 and-passes through conduit |23, cooler |24, and conduit I2l to another vaporliquid separator |20. Higher-boiling portions of the mixture 'originally passing as a gas through. conduit l2l and 0| 4will be in a liquid state after' this compression and cooling, andare separated in separator |20 from uncondensed gases and vapors. This liquid materialcontains appreciable quantities of propene and butenc and is removed from separator |20 through a conduit 16 tor l is operatedat s pressure'between about lighter hydrocarbon material.

300 and 850 pounds per square inch and, preferably, in the range of 500 to 750 pounds per square inch. Higher-boiling constituents of the vapors passing from separator |26 to conduit |30 are liqueed by this compression and cooling step, and are removed from separator |36 through a4 conduit |31, controlled by valve |38, and are reintroduced into' conduit |25 and separator |26. The material which remains uncondensed in separator |36 now comprises an apand contains only small amounts Iof heavier hydrocarbons. It will, however, contain anappreciable proportion of propene and butene, which should be recovered. This fraction passes from separator' |36 through-a conduit |40 controlledby' a valve 4| to an absorber |50.

, In the absorber |50 the gaseous material which is passed from` the separator |36, and which is now at an elevated pressure of the order of about '150 pounds per square inch, more or less, is contacted with the lean absorption oil introduced at the .top of the absorber through conduit |65. This absorption oil' is introduced in such amounts that essentially all the hydrocarbons having three and more carbon atoms -per molecule, which are present in the material `passing through conduit |40, are absorbed along with much of 'the The residue gas, containing principally hydrogen and methane,

passes from the absorber |50 through 'conduit |5|. The rich absorption o'il passes from the absorber |50 through conduit |52, controlled by valve |53, to heater` |54, and is sent through conduit |55 to the top of the stripper |56, which it enters at a low pressure, of the order of about to 50 pounds per square inch, and at an elevated temperature, which need not be in excess of about 225 to 250 F. In the stripper |56 the light hydrocarbons which have been absorbed by the oil in absorber |50 are removed vas a |65, controlled by a valve |66, to the top of the absorber |50. l

Lean residue gases passing from the absorber |50 through conduit |5| may be discharged from the system through valve |10, or a part of these gases may be diverted from conduit |5| through conduit |1|, controlled by a'valve |12, to the bottom of the stripper |56,.where they are in- 10 preciable concentration of hydrogen and methane ure 1 as to show the inter-connection clearly, and for these parts the same numerals have been used to indicate the same pieces of apparatus.

As was described in connection with the apparatus shown in Figure 1, a liquid hydrocarbon mixture containing C3 and heavier hydrocarbons,

`together with some llower-boiling material passes from the separator through conduit 46, con-v trolled by a valve 41, to a fractionating column 50. This fractionating column is supplied with suitable heating means, such as 'the heating coil 5| in the bottom, and a liquid charge stock to the accumulator and surge tank 203. A stream of low-boiling unreacted hydrocarbons, such as .Ca hydrocarbons, .is withdrawn in the liquid phase from the accumulator 52 through conduit 53, controlled by a valve 54, and is passed by pump 56 through conduit 51, and the expansion valve 58 to the cooler and condenser 20|. If desired, or necessary, some sort of cooling means may be interposed in conduit 51 subsequent to the pump 56, and with this modiiicaticn it may at times be possible to operate without the use of the pump 56 which may be by-passed by means not shown. In the cooler and condenser 20| this liquid hydrocarbon stream is partially orcompletely vaporized and produces thereby an appreciable cooling and refrigerating eiect.' This vvaporizing material is in indirect heat-exchangeA relationship with vaporsl passing from the top of the fractionating column 50 through conduit troduced to the stripper to aid in stripping the,l

remaining amount of absorbed hydrocarbons .from the oil just before itleaves Vthe stripper through conduit |51. `A gaseous material passes from the top of. the stripper |56 through a ccnduit |13, controlled by a valve |14, and nally is reintroduced into the system through valve |15 into conduit 30, where it is mixed with the emue`nt of the dehydrogenation operation.

In Figure 2 is shown amodied arrangement 200, as will be readily appreciated by those skilled in the art.

The expanded material passes fromthe' cooler and condenser 20| through conduit 2|0, and

passes through valve 2|| to conduit 44 and is reintroduced into the system. Ii desired, any 1 liqueiled in the cooler and 'condenser 20|, will accumulate at `thebottom'of the accumulator 203 and may be passed back to the fractionating column 50 through conduit 204, controlled by a valve 205, being pumped by pump 206 through l conduit 201 to the top portion c! the fractionof apparatus whereby our PIOCSSS may be IJI'B'G-v y ticed by'using an indirect heat-exchange relavapors passing from the top of the fractionating column or ply-feed stripper 50. This modiilcationis shown only with such necessary parts lof the arrangement of apparatus shown inFigvating column 50. Uncondensed material will be passed from the top of the accumulator 203 to a conduit 6|, controlled by a valve 62, and will be passed into the conduit |20, which contains gaseous material passing from the separator 45, as has been described hereinbefore in connection with Figure 1. The remainder oi the apparatus is the same as has been hereinbefore described in connection with Figure 1.

The operation of this modification of our process does not produce'results which aremarkedly diil'erent from the results produced when the first described modification is used. However. it does permit the advantageous use of the light unreacted hydrocarbons as a refrigerant in preparing a charge stock, or a subsequent conversion process without mixing this refrigerating material with the charge stock. While in many operations to which our invention may be adapted, it will be desirable to incorporate the material which makes up this refrigerant as a p'art of the charge stock to a conversion process, it may also often be desirable to secure the refrigerating effect of all of the stream before it is subjected to subsequent treatment. Thus, in the event that the light unreacted material is largely paraiiinic, it may be successfully used in the modification shown in Figure 2 as a refrigerant and then can be'passed from the system through conduit 212. If it is desired to recirculate this material to the process, it may then be passed to the dehydrogenation step, along with fresh charge stock which enters the system through conduit i0. In case this material contains an appreciable amount of olefin hydrocarbons, but too large an. amount of paraiiin hydrocarbons to make it desirable to introduce the stream directly to the polymerization process, the material which is passed from the system through conduit 2l! may be sent to olefin-paraffin separation 4means not shown, and the olefins separated from the parafiins and returned to the process through conduit 49, while the parafhns are mixed with fresh charge and introduced to the process through conduit I0.

The dehydrogenation step of the process may be either thermal or catalytic or a combination of both, but in any case it should be conducted at as low a pressure as will be practicable. Although a subatmospheric pressure may at times be most desirable, it will generally be more practicable to operate this step at a superatmospheric pressure which, however, should not exceed about 200 pounds per square inch and should be preferably only sufilciently high to insure adequate ow through the apparatus and provide a small superatmospheric pressure at the inlet to the com.- pressor Il'. When pressures near the upper part of this range exist in the tar separator 3| and when the cooler- I3 may be operated at a low temperature, such as a temperature of about 35 F. or even less, it may be possible to do away with the compressor Il, as will be appreciated by those skilled in the art.

The dehydrogenation catalyst, when one is used, will preferably .be of the chromium oxide type, such as those disclosed in U. S. Patents 1,905.383 and 2,098,959 (Re. 21,911), and in the copending application of Matuszak and Morey, filed November 9, 1937, Serial Number 173,708, now Patent 2,294,414, granted September 1, 194:2, or of the bauxite type, such as those disclosed in the copending application of Schulze, filed October 6, 1936, Serial Number 104.306, now Patent 2,167,602, granted July 25, 1939. With such dehydrogenation catalysts, the dehydrogenation temperature may be as low as about 750 F. but generally somewhat higher dehydrogenation temperatures, such as those of the order of about 850 to 1150 F., will produce the most desirable results.

If thermal dehydrogenation is to be employed, somewhat highertemperatures, such as up to about 1300 F., should be used, with a preferred range for thermal dehydrogenation lying between about 1000 and 1250 F. In any event, the reaction time should be such that between about 10 and 40 mol percent of the effluent consists of catalytically polymerizable olefins, and preferably about 20 mol per cent of such olefins, in order that secondary reactions of the dehydrogenation products do not take place to any appreciable extent in the dehydrogenating portion of the apparatus.

As has been mentioned hereinbefore, the polymerization which will take place in the apparatus diagrammatically represented as the vcatalytic polymerization chamber 10, may actually be either a thermal or catalytic processand may involve not only the polymerization of olefin hydrocarbons, but mayalso be operated to include in any known manner the reaction of olefin hydrocarbons with other hydrocarbons, such as paraffins, naphthenes, and aromatics, to produce desired hydrocarbons of higher molecular weights. .One very advantageous manner of operating this part of the process has been described by Frederick'E. Frey in his copending application Serial Number 305,549, filed November 21, 1939. In this modification, the hydrocarbon stream which passes from the fractionating column 50 to the conduit 65 contains substantially only propene and butene as the olefins to be reacted, and the polymerization is so operated that substantially all of the butenes are polymerized along with only a. portion of the propene which is present. With this modification the hydrocarbon stream passing from the top of the fractionating column 88 through conduit 95 contains propene in high concentratiomwith some propane being substantially the only other hydrocarbon present. When this is the case, the modification of apparatus shown in Figure 1 may be used, where this stream is introduced directly into the top of fractionating column 50, as has been described.

In modifications of the polymerization step;

wherein substantially all the light olefins such as propene are polymerized, and only the corresponding paramns remain, it will generally be more desirable to use an indirect method of cooling for the top of the fractionating' column 50 as has been described herein in connection with the modification shown in Figure 2. This may also be true in connection with a process wherein the polymerization step is a thermal one, although in this case the direct refrigeration shown in Figure 1 may be used, even though the hydrocarbon stream used as a refrigerant may have a low olefin hydrocarbon content.

As an example of the operation of one modification o! our process, a hydrocarbon mixture comprising substantially pure isobutane, along with not more than about 10 per cent oi' normal butane, was mixed with about 2% times as much recycled hydrocarbon material having substantially the same composition, and this mixtin'e was passed through the thermal dehydrogenation coils 2l, the catalyst chamber il not being in operation at this time. A dehydrogenation temperature in the coils 2l was maintained between about 1150 and 1220 F. and a gage' pressure of about 25 pounds per square inch was maintained 'at the exit of the dehydrogenation apparatus.

130 pounds per square inch and was passed at a temperature of about F. to the vapor-liquid separator l5. The condensed liquid, which con tom of the fractionating column was maintained at a temperature of about 105? F. by means of the heating coil i and the top was cooled to a temperature of about 60 F. by an introduction and vaporization of a substantially pure C: hydrocarbon stream, which contained about 50 per cent propene, through conduit 51 and the expander and vaporizer 60. The vapors nally passing from the top of the fractionating column 50 through the conduit 6I contained about 'I0 per cent of C3 hydrocarbons and about 6 per cent C4 hydrocarbons, the remainder being lower-boiling material, including about 17 per cent of methane.

The charge to the polymerization step, which was separated from a low point of the fractionating column 50 through conduit 65, consisted primarily of C3 and Ci hydrocarbons, with only about 1 per cent of Cz hydrocarbons, and contained substantially no methane or hydrogen. This stream had an appreciably higher ratio of Ca to C4 hydrocarbons tha n d id the hydrocarbon stream entering the fractionating column through the conduit 46. 'I'he Cshydrocarbons which were vaporized and passed from the fractionating column 50 through the conduit 6i were recovered in subsequent parts of the separating apparatus and were iinally brought back for inclusion in the polymerization charge stock by passing from separator |28 through conduit |21 as a liquid to separator 45 and thence, through conduit 46', to the fractionating column 50, so that the material passing through conduit 46 had a higher ratio of Cs to C4 hydrocarbons than ,did the effluent of the dehydrogenation.

The polymerization step was operated so as to polymerize substantially all of the C4 olefin hydrocarbons, along with an appreciable portion of the C: olefins and the eiliuent of the polymerization was passed to the debutanizer 13. The polymers were separated therefrom and dischargedto conduit 16. From the fractionatingeolumn, or debutanizer 13, the overhead vapors, which consisted primarily of C3 and C4 hydrocarbons, passed to the depropanizer 88 and therein a separation was madebetween the C: and C4 hydrocarbons. The C4 hydrocarbons passed from the bottom of the fractionating column through conduit 90 and were returned to the dehydrogena tion step, while the C: hydrocarbons passed from the fractionating column B6 as vapors and were cooled and condensed in the cooler and condenser 98 and passed therefrom to the accumulator 52 from which they could again be withdrawn to be used as a refrigerant.-

While in describing our invention we have illustrated'it by the use of certain specific examples, it should be understood that we do not intend that it should be limited by the specific details so used. We have shown certain modifications of operation and also shown certain limits within which successful operation m'ay be carried out, but various modifications will be apparent to those skilled in the art.

We claim:

l. A process which comprises passing a normally gaseous mixture containingl butenes, propene, hydrogen and methane to a separating means, passing to -said separating means propene vapors as subsequently recited, separating in said separating means a major portion of said hydrogen and methane, passing the residual mixture containing butenes and propene together with any residual minor proportion of unseparated hydrogen and methane in liquid phase to a fractional distillation means, withdrawing frcm said fractional distillation means a liquid polymerization feed stock consisting essentially of C3 and C4 hydrocarbons, including butenes and propene, the ratio of C: to C4 hydrocarbons in said stock being substantially greater than that of the charge passed to said separating means, subjecting said feed stock withdrawn from said fractional distillation means to catalytic polymerization to effect polymerization of substantially all of said butenes and a substantial portion of said propene, subjecting the polymerization eiiiuent to treatment to recover an essentially C; fraction of unreacted hydrocarbons containing propene, liquefying at least a portion of said unreacted propene in said C: fraction, passing said liquefied unreacted propene to saidfractional distillation means in heatexchange relationship with overhead vapors of said fractional distillation means to condense substantially al1 of the C4 fractions and at least a portion of the Ca fractions in said vapors and concomitantly to vaporize at least a portion of said liquefied propene, passing the propene thus vapcrized to said separating means and utilizing said condensed fractions as refluxing liquid in said fractional distillation means.

2. A process as defined in claim l. in which said heat-exchange relationship is direct heat exchange and in which said vaporized propene and uncondensed vapors from the fractional distillation means are passed together in a common stream to said separating means.

3. A process as defined in claim l, in which said heat-exchange relationship is indirect heat exchange.

4. A process for producing normally liquid hydrocarbons by polymerization of propene and isobutene, which comprises passing into the middle section of a fractionating column in liquid phase a normally gaseous hydrocarbon mixture containing propene and isobutene and smaller amounts of lighter undesirable hydrocarbons,

' withdrawing from a low point in the column a said unreacted propene in said fraction,

liquid polymerization feed stock consisting essentially of C: and C4 hydrocarbons, including propene and isobutene, that is substantially free from lighter hydrocarbons, the ratio of Ca to C4 hydrocarbons in said stock being substantially greater than that of the charge to said column, subjecting said feed stock to catalytic polymerization to effect polymerization of substantially all of said isobutene and a substantial portion of said propene, subjecting the polymerization eilluent to separation to separate an essentially Cs fraction of unreacted hydrocarbons containing the unreacted propene, liquefying at least a portion of and discharging said liqueiled -unreacted propene into the top of said column in direct and intimate heat-exchange relationship with the vapors therein to act as a reflux and refrigerant therefor, allowing the unvaporized portion of said liqueiled unreacted propene to descend said eolumn and enter said polymerization feed stock, recovering the vaporized portion of said unreacted propene and introducing it to the middle section of said 'column in admixture with the feed thereto.

5. A process which comprises the thermal dehydrogenation of isobutane to form an eiiiuent v of a fractionating column,

to catalytic polymerization to effect polymerization of substantially all of said isobutene and a substantial portion of said propene, subjecting the polymerization eiiiuent to treatment to recover an essentially C: fraction of unreacted hydrocarbons containing the unreacted propene, llquefying at least a portion of said unreacted propene in said fraction, and discharging said liquefying unreacted propene into the top of said column in direct and intimate heat-exchange re lationship with the vapors therein to act as a reux and refrigerant therefor, allowing the unvapmjaeiportion .of said liqueed unreacted popene to descnd 's'aid columnandY enter saidpglyf ,.7

merization feed stock, recovering the vaporized portion of said unreacted propene and introducing it to the feed stock to said column thereby to increase the C: to C4 hydrocarbon ratio thereof over that of said residual emuent.

6. A process which comprises the thermal dehydrogenation of isobutane to form an eluent containing isobutene, propene, hydrogen and methane, hydrogen and methane in a separating means, charging the residual emuent in liquid phase into the middle section of a fractionating column, withdrawing from -a low point in the column a liquid polymerization feed stock consisting essentially of Ca and C4 hydrocarbons, including propene and isobutene, that is substantially free from lighter materials, the ratio of Cs to C4 hydrocarbons in said stock being substantially 1 greater than that of the eiliuent from said dehydrogenation, subjecting said feed stock to catalytic polymerization tial portion of said propene, subjecting the polymerization eiliuent to treatment to recover an essentially C: fraction of unreacted hydrocarbons containing the unreacted propene, liquefying at least a portion of said unreacted propene in said fraction, and passing said liqueed propene-containing fraction in indirect heat-exchange relationship with the vapors issuing from the fractionating column to allow the C: hydrocarbon fraction to expand and thereby act as a refrigerant for the vapors issuing from the fractionating column'. thereby condensing substantially all of the C4 fractions and at least a portion of the C: fractions in said vapors, returning condensed portions of the vapors to said fractionating column as a refiuxing medium. and passing the expanded liquefied propene-containing fraction to the separating means.

HARRISON L. HAYS.

JOSEPH L. MAHER.

separating the major portion of said' to` effect polymerization of' substantially all of said isobutene and a substan- CERTIFICATE oF. CORRECTION., Patent NC. 2,551,125. June 15, 192111.

HARRISON L. Rus, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 58, for "isobuta'ne" rend 'isobutene; page 8, first column, line 21,v Claim 5, for "liquerying" read #liquefied-q and thm: the sam Letters Patent should be' read with this correction therein that the same mayv conform to the record ofthe ca se in the Patent Office.

Signed and sealed this 12th day of' September, A. D. 19h11.

Leslie Frazer (seal) Acting commissioner of Patents. 

